Minimally invasive medical techniques are intended to reduce the amount of tissue that is damaged during interventional procedures, thereby reducing patient recovery time, discomfort, and deleterious side effects. Such minimally invasive techniques may be performed through natural orifices in a patient anatomy or through one or more surgical incisions. Through these natural orifices or incisions clinicians may insert interventional instruments (including surgical, diagnostic, therapeutic, or biopsy instruments) to reach a target tissue location. To reach the target tissue location, a minimally invasive interventional instrument may navigate natural or surgically created passageways in anatomical systems such as the lungs, the colon, the intestines, the kidneys, the heart, the circulatory system, or the like. In existing systems, electromagnetic (EM) navigation may be used to track the movement of interventional instruments through a patient anatomy. Although EM navigation systems are useful for many procedures, they may be subject to magnetic interference from other equipment in the surgical suite. For example, a C-arm of a fluoroscopic imaging system or metal instruments may generate magnetic interference with EM navigation systems, causing unacceptable errors in the tracking of an interventional instrument. Improved navigation systems and methods are needed for tracking interventional instruments in surgical environments, including in environments where EM navigation is not suitable or may be compromised.